The present invention relates to a variable length packet switch, more particularly to a variable length packet switch for exchanging variable length packets such as a Common Part Sublayer (CPS) packet which is defined as an Asynchronous Transfer Mode (ATM) Adaptation Layer type 2 (AAL type 2).
When a signal such as a voice signal which is a low speed signal and must be transmitted with a little delay, is transmitted through a packet network such as an ATM network, a transmission delay due to a time for constructing a packet is produced. In order to improve such delay, a cellularizing system called the AAL type 2 (AAL2) has been recommended as a International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) recommendation I.363.2. This is a system for superposing a connection in an AAL2 level on a Virtual Channel (VC) connection in an ATM. In the AAL2, used is a variable length packet called a CPS-packet to which a connection identifier called a Channel Identifier (CID) is given. In the CPS-packet, a packet having a different CID is multiplexed and packed in a VC connection. Hereupon, it should be especially noted that a plurality of CPS-packets having different CIDs are multiplexed and packed on each other in a single ATM cell.
FIG. 14 illustrates a format of the CPS-packet. Referring to FIG. 14, a CPS-packet 1700 comprises a CID area 1701, an Length Indicator (LI) area 1702, a User-to-User Indication (UUI) CPS area 1703, a Header Error Control (HEC) area 1704, and a CPS Interface Data (CPS-INFO) area 1705. The CID area 1701 is the one on which the above described CID is loaded, and the LI area 1702 is the one in which a packet length of the CPS-packet is stored. Furthermore, in the UUI area 1703, a code called a user-to-user identifier is stored. The HEC area 1704 is the one for controlling an error of a packet header. The CPS-INFO area 1705 is a pay load of the CPS-packet and able to change its length. An ITU-T recommendation I.366.2 is made for a method to use the LI area 1702 and the UUI area 1703 in the foregoing ITU-T recommendation I.363.2, which is described in detail according to the method to use special packets and the CPS-INFO area 1705.
Hereupon, a method to constitute a switch in the AAL2 level is important. As was shown in the foregoing description for the prior art, CPS-packets having different CIDs are multiplexed and packed in a single cell. Accordingly, in order to output the CPS-packets multiplexed and packed in the single cell to different paths, it is necessary to decompose the ATM cell once. Moreover, after the received cell is decomposed, the CPS-packet is switched, and the cell is cellularized again, so as to transmit the cellularized, cell. Hereupon, in the case where the CPS-packet is switched, a method in which one CPS-packet is loaded on one ATM cell to allow it to pass through a switching section is conceived. However, the CPS-packet is a variable length packet, and if the CPS-packet is short in length, an ineffective area is produced in a payload of the ATM cell, so that a capacitance of the switching section is sometimes limited.
In order to solve the foregoing subjects, the object of the present invention is to provide a variable length switch which exchanges CPS-packets by AAL 2 effectively without limiting capacitance of a switching section when the CPS-packets loaded on an ATM cell are exchanged. The object of the present invention is to suppress a necessary bandwidth of the switching section not by performing switching after loading a single CPS-packet on a single ATM cell, but by multiplexing and packing a plurality of CPS-packets on the single ATM cell which are outputted to the same output path.
Furthermore, an interface section distinguishes special sorts of CPS-packets from others, and allows them to travel on a different connection and to pass through the switching section, thus enabling to control a transfer quality such as a loss rate in accordance depending on characteristics of the CPS-packets. This implies that a quality control of the special CPS-packets in the switching section is enabled when a plurality of CPS-packets are multiplexed and packed in a single ATM cell and allowed to pass through the switching section.
According to the present invention, a variable length packet switch is provided, which exchanges a plurality of variable length packets loaded on a cell to be transferred in an asynchronous transfer mode, comprising:
a receiving interface section for receiving a cell;
a transmission interface section for transmitting the cell; and
a switching section for exchanging the cell, the switching section to which the receiving and transmitting interface sections are connected,
wherein the receiving interface section includes a variable length packet receiving section which disassembles the received cell to demultiplex and unpack the variable length packets multiplexed and packed in the received cell and multiplexes and packs the variable length packets in a cell having the same header value, the variable length packets being transferred to the same transfer interface section where a transmission processing is performed, thereby allowing the variable length packets to pass through the switching section,
the switching section transfers the cell transferred from the receiving interface section to the transmission interface section where a transmission processing is performed in accordance with a header value of the cell, and
the transmission interface section includes a variable length packet transmission section which disassembles the cell transferred from the switching section, demultiplexes and unpacks the variable length packets multiplexed and packed, and multiplexes and packs the variable length packets to be outputted in the same output path in a transmission cell having the same header value.
In the variable length packet switch of the present invention, the receiving interface section further identifies a sort of the variable length packet having the same transmission interface section where a transmission processing is performed, and multiplexes and packs the variable length packet in a cell having a different header value depending on the sort thereof thereby transferring the cell to the switching section.
In the variable length packet switch of the present invention, an upper layer function section connected to the switching section is further provided, wherein the receiving interface section disassembles a received cell, demultiplexes and unpacks the variable length packet multiplexed and packed in the received cell, and multiplexes and packs the variable length packets, which are to be subjected to a transmission processing by the same upper layer functioning section, in a cell of the same header value, thereby transferring the cell to the upper layer functioning section.